This invention relates to automatic watering apparatus for growing plants, particularly potted plants, by means responsive to dampness of the soil or growing medium watered thereby. Dampness of the soil or growing medium is sensed in comparison with `field capacity,` which is a condition in which the soil is saturated to the point where it can hold no more water against the pull of gravity. The dampness requirement varies with different plants, and in most all situations is a condition substantially less than field capacity, it being a general object of this invention to control soil dampness as may be required.
`Field Capacity` refers to a condition in which each soil particle holds the maximum amount of water film against the pull of gravity, the amount of air space in the soil being low. As plant roots and evaporation withdraw water from the soil, the film of water becomes thinner and more space is gained for soil air. When the film becomes so thin that its molecular attraction to the soil particles is stronger than the root tips ability to extract it, the plant will wilt even though some water remains in the soil. During the stages in which soil dries from field capacity to the wilting point, the plant has sufficient water for healthy growth. Field capacity varies by soil type; clay soil with many fine particles holds more water than sandy soil with fewer, courser particles, and loamy soils which contain a mixture of particle sizes have an intermediate field capacity.
Heretofore, automatic and self watering devices for potted plants have involved wicks, water transfer tubes, and air displacement tubes controlled by porous elements, and characterized by complexity and subject to malfunction due to clogging of the water tube and/or air tube. And, with the use of wicks alone it is difficult- to control soil moisture levels.
The Crane Jr. U.S. Pat. No. 3,758,987 issued Sept. 18, 1973 is an example of the prior art, wherein a moisture sensor buried in the soil controls the entry of displacement air into a substantially airtight tank permitted to discharge water into the soil through a filter. Though the Crane Jr. principle is workable, it is subject to malfunction due to the passage of some water through the porous element, so that the air tube becomes clogged with the accumulation of water which cannot be readily displaced by the available pressure differential. That is, the porous element of Crane Jr. allows water to collect in the air transfer tube supplying air to the closed water reservoir. Another problem with the Crane Jr. principle is that a meniscus will form near the discharge filter and thereby obstruct the flow of water into the soil or growing medium. It is therefore an object of this invention to eliminate the entry of water into the air transfer tube, by the provision of a protective air suction control means, and to preclude said meniscus, and to these ends I provide a hydrophobic element following the aforesaid hydrophilic element, and preferably with a liquid entrapment chamber therebetween.
The Endling U.S. Pat. No. 4,344,251 issued Aug. 17, 1982 is an example of the prior art, wherein a water transfer wick is buried in the soil for the gradual delivery of water therethrough, but lacking a method of restraining the flow of water between the reservoir and soil or growing medium. Consequently, water delivery into the soil will continue until field capacity is reached, which is deleterious to most all plants. Therefore, it is an object of this invention to combine wick water transfer with the aforesaid air suction control means, and to this end I provide a wick water control means responsive to the controlled delivery of supply water to effectively immerse and wet and saturate the wick for water transfer as circumstances require. Accordingly, the wick does not continuously transfer water, but is responsive to the soil dampness as sensed by the air suction control means.
Experiments with various types of wicking products indicated natural fibrous materials deteriorated within a few months. Materials displaying the greatest longevity were made of polyester or bonded acetate. It was also noted that the density of the wicking material determined the rapidity at which fluid was transferred. For example, the bonded material originally used as ink reservoir material as produced by American Filtrona in Richmond, Va. can easily transfer a liter of water, not containing particulate material, per hour.
During tests in which porous hydrophilic materials were evaluated, it was discovered that the pores in this material became encumbered quickly when a several cubic centimeters of soil water flowed through the porous rod into the air tube as would occur in the daily use of the Crain Jr. patent. Dramatically restricting the flow-through characteristic of the air valve by placing a hydrophobic membrane behind the hydrophilic rod significantly increased the length of time the air valve continued to function.
The air suction control means and the wick water control means can be embodied in a variety of ways, directly into the garden soil or into the growing medium of a planter box or pot. As shown and described herein, a potted plant is under consideration, with the automatic wick waterer means conveniently arranged for discharging water into the bottom of a pot and subject to control by the dampness of the growing medium surrounding the plant root system within the pot. In accordance with this invention, the waterer is a unit which is applicable to installation within a planter pot containing soil or growing medium, or it is applicable as a platform upon which a potted plant is supported. Accordingly, it is an object of this invention to provide a water supply unit suitable for either inside or outside use, with respect to a planter pot, and a unit which incorporates both the air suction control means and the wick water control means. In practice, the water supply container is a flat closed vessel of round form to be set into or beneath a pot of complementary round form. Being flat, the vessel is shallow so that the head of water pressure is commensurately slight, however, it is existent and subject to delicate control by the aforesaid air suction control means. This slight pressure and delicate control has its advantageous results in the function of the wick water control means, all as hereinafter described, there being a delivery water level movement that raises and lowers the water for immersion or retraction of the lower end of the wick exposed thereto.